Compensating means for oscillating radio circuits



May'22,1928. v I 1,670,586

w. LYTTON COMPENSATING MEANS FOR OSCILLATING RADIO CIRCUITS Filed March so, 1925 v 2 Sheets-Sheet 1 INVENTOR.

h a/fer Z5070 A TTORNE Y.

May 22. 1928.

w. LYTTON COMPENSATING MEANS FOR OSCILLATING RADIO CIRCUITS Filed March 30, 1925 2 Sheets-Sheet 2 Fig.5

INVENTOR: WALTER LYTZTION A TTORNE Y.

-Patented May 22, 1928.

UNITED STATES WALTER LYTTON, OF CHICAGO, ILLINOIS.

COMPENSATING MEANS FOR OSCILLATING RADIO CIRCUITS.

Application filed March 30, 1925. Serial No. 19,259.

This invention relates to radio receiving systems and it has for one of its objects providing a method for reducing and largely eliminating the oscillating tendency of radio circuits, particularly when tuned radio amplifications of several steps are used. Another object is to provide suitable means for carrying out the method. A further object is to provide a method and means therefor for compensating forany oscillating effects of the system which may not be eliminated, the purpose being to obtain the benefits of the system which ordinarily produce oscillations without any of the disadvantages thereof. Other objects of the invention will be apparent from a consideration of the accompanying drawings and thefollowing description thereof:

Of the drawings Fig. 1 is a diagrammatical View of a radio system which embodies some of the features of my invention; Fig. 2 is a detail view of certain devices used in the system; Fig. 3 is a diagrammatic view of a modified system; and 4 illustrates a further modification which involves the heterodyne principle.

As is well understood, when high frequency radio waves are materially amplified, especially when several steps of tuned radio are used, the oscillating tendency of the system often offsets any advantage obtained by the increased amplification. Means have been provided for neutralizing the oscillating tendency of such systems. But the use of such means tends to eliminate certain advantages whichmay be obtained by systems which have "the oscillat ing characteristics. One method of preventing abnormal oscillations consists in neutralizing the capacity of the electrodes of the amplifying tubes by external means so that the input and output circuits may be tuned without serious objectionable coaction on each other. Another method consists in detuning the input and output circuits so as to reduce or eliminate the oscillating tendencies. By the use of the invention I am able to obtain the advantages of both of these systems and at the same time to eliminate the disadvantages thereof.

This undesirable oscillating tendency is owing to the capacity effect of the electrodes of the vacuum tubes in conjunction with the tuning of the input and output circuits tov the incoming frequencies. Any detuning of the two circuits will tend to decrease the ductance coil 15.

oscillating tendency, and, by variable means for detuning, the tendency can be greatly reduced. My method consists in thus reducing the oscillating tendency and in eliminating any disadvantages of this detuning process and-also of any remaining oscillation effects.

In applying my invention to the detuning method of reducing oscillating tendencies, any ordinary radio system may be used. I prefer for the purpose an antenna or loop 10 with the variable inductance coil 11 acting as a primary for the input circuit coil 12 of the receiving tube 13. put circuit 14; of this tube has a variable in I prefer to vary this inductance by means of taps 16 and a contact member 17. As is well understood, if in practice the inductance coil 11 is -substantially tuned to the incoming waves, and, with tuned radio frequency, the input and the output circuits are also substantially tuned to incoming waves. By having the coil 15 variable not'only may the output circuit be tuned to the incoming waves if so desired, but, in carrying out my invention, this coil is detuned so as to decrease the oscillating tendency. Similarly with the amplifying tube 18, the coil 15 of the output circuit 19 is variable and the circuit thereof may be detuned with reference to the incoming oscillations.

\Vhen the tube output circuits are thus detuned, no matter how slightly, aside from the advantage of reducing local oscillating tendencies, there is always a disadvantage in that oscillations of the modulated carrier waves are not transmitted through the system as effectively as is the case when the output circuits are tuned. Not only is there a slight decrease in the energy of the modulated oscillations which it is desired to transmute into audio waves, but also the ratios of the amplitudes of the oscillations are decreased. As is well understood, the audibility of the oscillations depends upon the amount of change in amplitude of the modulated oscillations, as well energy thereof; and, if the amplitudes are reduced proportionally by detuning or otherwise, the change in the ratio of the maximum to the minimum amplitudes will be reduced at a much greater rate than the energy. I, therefore provide means for compensating for the disadvantage of the detuning on the modulated oscillations, and

The outus upon the also for any undesired oscillating tendency which may be left, it being understood that any local oscillations tendto mask the incoming modulated oscillations.

:- is more or less negligible.

masked by the locally generated oscillations and are not dampened by the detuning means =he variations, by my method: in the impedances of the input circuits, however, arenot brought about by direct variations in theinductance or the capacities of the circuits involved, but by the applicationto such circuitsof external influences.

Any suitable means may be used in: carrying out the method, but the particular meanswhich I prefer for this purpose comprises a circuit 20 which consists of a closed circuit with an inductance coil 21 therein. This coil is inductively associated with the secondary 22 of the input orgridcircuit 23, which has; an ordinary tuning condenser 24. In practice I mount coils 15, 22 and 21 end: on, as'indicated in Fig. 2, so that the coils v15 and 22 are inductively related, and the coils22 and 21 are also so related, but the inductive effect'between the coils 15 and 21 It will beseen that, if these coils are so arranged and prop erly associated, the coil 21 will assist the coil 15 in building up its magnetic field in the: coil 22, as the coil 21 will decrease the neutralizing tendency of the coil 22: on the field of the coil 15. As a consequence the magnetic change in the coil 22 will be increased and thepotential generated bythe coil22', and hencethe potential of the grid, will' be increased and a secondary tendency will be a decrease in the current flowing through the output circuit '14.: owing" to the opposing increased magnetic change in the coil In this manner the energy and the ratio of the amplitudes of the carrier and modulated oscillations maybe so increased as-tov entirely compensate for the dampening tendency of the det-uning and the oscillating tendency ofthe system as a whole. And by thus influencing by external means, the impedance of the input circuit, the resonance frequency of the input circuit remains unchanged.

By making adjustable the inductive eilect ofthe coil 21 on the coil 22 the best resultsma 1 be produced. This inductive efiect of the coil may be varied in any'suitable manner. I prefer to shift the coil 21'coaxially towards. or away from the 005.1122. In this manner the tuning of the output circuits to to the other groups.

the incoming oscillations may be approachedsuificiently toobtain substantially full value thereof without producing greater oscillating tendencies than can be compensated for by the coil 21. ,rrnd I find in practice that, by properly shifting the coil 21, a position will: be reached where the audibility of the sound waves will be materially greater than without the coil and at the same time the current consumption of the corresponding output circuit will be materially reduced.

Inasmuch as the capacities of the coils 21 are very small relative to the inductance, the oscillating-tendency of the current therein is' also small and substantially negligible compared with thehigh frequency of the carrier waves. As a consequence, any tendency to produce: abnormal local oscillations, will: be offset by these coils, as the coils will absorb the'back electromotive force of the grid circuit before it can induce a current in I the plate circuit. It will be understood that, as the compensating coils thus act in a sense as absorbers of energy, these coilsmust h'ax e an inductance small compared with that of the grid circuit so as not toabsorb the modulated oscillations, butrather to increase the amplitude thereof as described.

It has been: found'in' practice that these various effects of the compensating coils require sensitive adjustments thereof and suitable designing of the coils with reference to their electric characteristics. 'llot only should the inductance of the coils be small, but the inductance in the different coils should increase with the number of tuned radioamplifying tubes because, as theamplification increases, the oscillating tendencies increase. Also the coupling of these coils with the coils. 22 should be Varied according: to the number of tubes. As a consequence of all this itbecomes desirable not only to properly design the coils, but also to adjust the. coupling relation of each compensating coil with its associated grid coil, with reference to the amount of inductive effect upon each other, and'also with.

reference to the; amount of detuning by meansof the coils 15;, In other words, each group of coils, 15,22 and-21,should be prop erly adjusted with reference to 'each other, the. adjustment usually varying with the tubes. This having been done eachgroup ofcoils thenshould be adjusted with reference That is, the compenv sationr is cared for by adjustmentof the individual coils in eachgroup and the system is then. properly balanced by adjustingeach group with reference "to the other groups. In viewof this and the resulting decrease in'the current output circuits, the system may be described as" anon-oscillating, low current loss, group compensating, radio frequency amplification system.

Any suitable means may be used for ad- Inn justing the relation of the coils 21 to the coils 22, and the angular relation or the distance may be varied as desired. I prefer for the purpose mountin the coils 21 and 22 end on, or coaxially, l ig. 2, and so that'thecoils 22 may he slid axially; and for this purpose a screw 28 may be fixed to each coil and threaded into a fixed bearing, 29. Inasmuch as the function of the coils 21 is not materially aiiected by the frequency of the incoming waves, it is usually unnecessary to vary the position of these coils when the frequency of the incoming waves changes. The coils may be set with reference to the coils 22 so as to produce the best result with one ordinary frequency and they will be substantiall' in osition for the best result with other frequencies. Hence in practice the coils are preferably adjusted when the system is assembled and they are then permanently fixed in position by any suitable means such as a set screwBO.

The inductance of the coils 15 may be varied in any suitable manner. As stated hereinabove I prefer to have taps 16 leading from these coils which are suitably connected to the circuits by means of cont-act pieces 17 operated by'dials 31, the dials being mounted on the dial board of the cabinet. As explained herein, the inductance of these coils is varied so as to detune the output circuits of the tubes. Necessarily, for this purpose, variations in the inductance are required when the incoming frequency varies, and also material variations are. required when the changes aremade from an aerial antenna to a loop.

As stated herein-the systems which I have provided may be used either with an aerial or a loop. IVhen a loop is used ordinarily the contact pieces 17 are shifted to the leads 32 so as to have the full inductance of the coil. The condensers 2% may be independently operated by the knobs 33. Any suit-- able audio amplifying system may be used with this system, such as the one illustrated comprising the detector tube 25 and the audio tubes 26 and 27. 7

Although I have hereinabove described with much particularity my method as ap plied to a system in which the output circuits may be 'detuned with reference to the incoming frequencies, as much as may be desired; yet it is to be understood that my method may be applied to systems in which the output circuits have no harmonic relation to the incoming frequency. The output circuits in fact may be aperiodic; and the carrying out of my method will not be materially changed; the function of the compensating coils 21 will still be as herein described.

In Fig. 3 I have illustrated a system which embodies features of .my invention and which consists in the use of three tuned radie amplifying tubes. In conjunction with either of these systems other radio amplify ing tubes may be used, and also several audio amplifying tubes. In this system I use also two audio amplifying tubes. This system comprises the aerial or loop antenna 3-55, the

1 the ocradio amplifying to. es 36, 37 and no tcctor 39, and the audio amplifying and 41; also the adjustable output circuit coils 42, 43 and 44C, and the input (ll'i 46 and IT, and 48 each arranged to be tuned to the incoming frequency. Associated with the respective coils of the input circuits at}. 47 and 48 are the compensating coils 5U, 51 and 52. r ind in the input circuits are the adjustable condensers 53, 5i, 55, and 56. In asmuch as, in this system, three tuned radio tubes are used, the desirability of coinpem sating means for the oscillating tendency greater. But by the use of the compensating coils as hereinabove explained the addition of the extra tube is found to have no disadvanta. e and materially increases the loudness of the sounds which are ultimately produced. Fig. 3 shows the coils of the adjacent output and input circuits in parallel, merely for compactness. It is to be understood, however, that the rclative positions of the two coils in each of these pairs may be varied as the e:-:igenci -:s of the case may require. As stated hereinaboye I prefer to use them end on or coaxially.

In Fig. l I have illustrated a further modilication in which three radio amplifying tubes 60, 61 and 62 are used in conjunction with variable or aperiodic output circuits and compensating coils for the tuned input circuits, as herein-above exp; er. In this system I use a tube 63 for generating local oscillations to form beats with the incoming waves. The incoming waves and the local. oscillator, pass their oscillations into the grid circuit 81 of the amplifying tube 68. And the resultant of these combined oscillations is of the frequency desired. Following the tube 68 is the amplifying tubes 69 and a detector 70, and such audio amplifyin tubes as may be desired. These latter can be connected in any ordinary manner to the output circuit 71 of the detector 70.

In carrying out my method with this system I employ the compensating tubes 71 and 72 and 73 in conjunction with the input circuits 74-, 75 and 7 6, respectively, in the manner hereinabove described with reference to the other systems, and also employ the coils 77, 78 and G l as explained. However, the frequency of the resultant oscillations may be made the same for any incoming frequency. So that when the remaining portion of the system is properly adjusted for the frequency of the resultant oscillations no further adjustment is needed when changes in the incoming oscillations occur, Hence the output and the input cirllt) cuits 80 and 81 of the respective tubes 67 and 68 are tuned substantially to the incoming beat frequency, and an inductance circuit 82 compensates for such slight detuning as maybe necessary to avoid serious oscillations. The following output; and input circuits, however, may be designed for the particular resultant frequency which is to be used, and no further adjustments of the impedance of these circuits are required. The compensating coils 83 and S however, are used to compensate for oscillating tendencies', but may oe adjusted permanently tor all incoming frequencies.

In this instance I prefer to use, instead of the ordinaryv grid leak and condenser, in the input circuit 85 of the detector tube 70, inductance coils 86 and 87 having a core 88, one end of the coil 86 being connected to thecoil 89 of the input circuit and one end of the coil 87 being connected to the grid 90, the other ends of the coils being disconnected.

. In this system 1 show an aerial antenna 91 and a loop 92 either of which may be connected up with the sysem by means of any ordinary switch means, it being understood that the adjustments in the inductance of the coils 77, 78 and 6d may be made to meet the, requirements of the change. For instance the first four contacts of the coils 77, 78 and G l may be used with the aerial, and the contacts 93 may be used with the loop.

In carrying out my invention and also for use with many ordinary radio circuits,

it is sometimes desirable to increase the capacity 01": the antenna circuit by inserting in shunt therewith a condenser. For this purpose I providethe adjustable condenser. 95, Fig.8, which is; connected in parallel with the coil 34. With this condenser the capacity of the antenna circuit can be ad usted to suit the partleular antenna andvincoming waves. In order to reduce the amount or shunted energy I proide a choke coil 96 in the condenser line, and the permeability of the magnetic field of this coil can be adapted to the general needs or the circuit. Also in order to assist in suitably balancing the various devices of the circuits 1 provide an inductance coil 97 the inductance of which may be varied by the contact member 98. This inductance is connected in thecircuit so and thus materially, but adjustably, increases the inductance. Hence the ratio of the inductance of the two may be adjusted to an amount substantially the same asthe corresponding ratio of the other radio transformers, and the amount of variation of the adjustable condenser 53, for oiven angular rotation, may be made substantially or exactly the same as that of the condensers 54, 55, and 56. In this man nor the condenser 53 may be adjusted simultaneously with the other condensers and by the same operating means if desired.

I claim as my invention: In radio receiving system three inductively and coaxia-lly mounted coils, the central coil being connected'with an input circuit of said system, an end coil being connected with an output circuit of said system,

said third coil being connected in a mechanically independent circuit, and means for varying the inductive relation of said third coil to said central coil, said means comprising means for sliding said coil axially towards said central coil; I V

In testimony whereof, I hereunto set my hand.

WALTER LYTTON.

circuits of thereceiving transformer 

